Estimation of the size of air emboli detectable by electrical impedance measurement |
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Authors: | Email author" target="_blank">S?NebuyaEmail author M?Noshiro B?H?Brown R?H?Smallwood P?Milnes |
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Institution: | (1) Department of Clinical Engineering, School of Allied Health Sciences, Kitasato University, Japan;(2) Medical Physics & Engineering, University of Sheffield, Royal Hallamshire Hospital, UK |
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Abstract: | Non-invasive detection of air emboli in blood is investigated in vitro using a tetrapolar electrical impedance measurement.
A cubic tank with a linear array of four electrodes, spaced approximately 1 cm apart down one side, was filled with 0.2 Sm−1 saline. Bubbles were generated by carbon dioxide gas. Electrical transfer impedance was measured every 8.2 ms at 1.25 MHz.
The movement of bubbles was recorded by a video camera, and their sizes and depths from the middle of the array were measured
using captured video images. Changes in transfer impedance caused by passage of bubbles were clearly observed and almost identical
with those calculated theoretically. Using lead field theory and experimental results, the fundamental limit on the detectable
size of bubbles was estimated at the carotid artery, the great saphenous vein and the cephalic vein. The theoretical results
showed that a 0.5 mm diameter bubble is detectable at a depth of 5.3 mm, similar to the depth of the great saphenous and the
cephalic veins, and a 2.3 mm diameter bubble is detectable at a depth of 21 mm, similar to the depth of the common carotid
artery. |
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Keywords: | Electrical impedance measurement Biological tissue Air emboli Bubble Non-invasive detection |
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